Retreaded tires are readily available and provide an economical way to gain additional use out of tire casings after the original tread or retread has become worn. According to a conventional method of retreading, sometimes referred to as cold process retreading, worn tire tread on a used tire is removed by a special buffing machine that grinds away old tread and leaves a buffed surface to which a new layer of tread may be bonded.
Removal of old tread from the tire casing provides a generally smooth treadless surface about the circumference of the tire casing. The tire casing may then be examined for injuries, which are skived and filled with a repair gum. After completion of the skiving process, the buffed surface may be sprayed with a tire cement that provides a tacky surface for application of bonding material and new tread. Next a layer of cushion gum is applied to the back, i.e., the inside surface of a new layer of tread, or alternatively, the layer of cushion gum is applied directly to the tacky surface on the tire casing. Conventionally, the cushion gum is a layer of uncured rubber material. The cushion gum and tread may be applied in combination about the circumference of the tire casing to create a retreaded tire assembly ready for curing. Alternatively, a length of tire tread is wrapped around the tire casing with the cushion gum already applied. The cushion gum forms the bond between the tread and the tire casing during curing.
Following assembly of the tire casing, cement, cushion gum and tread, the overall retreaded tire assembly is placed within a flexible rubber envelope. An airtight seal is created between the envelope and the bead of the tire. The entire envelope tire assembly is placed within a curing chamber, and subjected to pressure and a raised temperature for a specific period of time. The combination of pressure, temperature, and time binds a layer of cushion gum to both the tire casing and the new tire tread.
The above-described method of cold process retreading is often accomplished on a tire builder. Conventional tire builders include a spindle on which a tire is mounted and a spindle on which a roll of tire cushion gum is mounted for dispensing. Typically the cushion gum may be dispensed by hand as the tire is rotated to adhere the cushion gum to the tire casing.
In certain applications, it may be advantageous to eliminate the spray cement completely. This may be particularly true in geographical areas where there is increased regulation of the use of chemicals within spray cement products. Further, use of spray cement can also add to the cost of producing retreaded tires due to the product cost and equipment cost. Various solutions to enable a cementless process have been suggested, for example, extruding heated cushion gum directly to a tire casing. This process however, is costly due to equipment costs and is unnecessarily complex.
After the cushion gum has been applied, the circumference of the tire casing with cushion gum is measured and an applicable length of tread is measured out, conventionally on a separate bench. The tire tread is manually cut to length.
In all tire building systems once the cushion gum has been applied and the tread has been cut to length, the tread must be applied to the cushion gum and casing. Due to errors in the cut length of the tire tread it may be desirable to stretch the tire tread around the perimeter of the tire casing and cushion gum in order to create an appropriately sized splice.
Further, it is often desirable, for aesthetic and structural strength purposes, to match the tire tread design at each end of the tire tread length so that where the two ends of the tire tread length match at the splice, the repetitive pattern of the tire tread design is substantially continuous. To create such a splice, it may be necessary to stretch the tire tread around the circumference of the tire casing and cushion gum because the tire tread length may have been cut to an extra shortened length in order to cause the matching of the tire tread design at the two ends of the tire tread.
Accordingly, there is a need for an integrated tread bench that combines the processes of cushion application, tread cutting and tread application into a single work bench machine while semi-automating the plurality of steps required to produce a finished retread tire prior to curing. There is also a need for a cushion gum application process and apparatus that controls the stretch of the cushion gum during application to the tire casing. Further, there is a need for a method and apparatus for applying cushion gum to a tire casing that uses a cementless application and stitching process. Further, there is a need for a semi-automatic method and apparatus for cutting an appropriate length of tire tread. Further still, there is a need for a semi-automatic method and apparatus of applying tire tread in a controlled stretch to a casing with an applied cushion gum to produce a tire with a predetermined range of splice size. Yet further still, there is a need for a semi-automatic method and apparatus of cutting and applying tire tread lengths such that the periodic tire tread design is substantially continuous in the retread tire.